Pretend for a moment that you're not tough — you're kind of wimpy, actually, with no defense mechanisms at all. That's all well and good if you're lying on your couch right now, peacefully reading this on your phone, but pretend you're in 6th grade: The only really big downside to not being tough in middle school is that you get picked on. For a lot of animals and plants on this planet, getting picked on means you get eaten, which is generally what animals are out here every day trying to avoid.
But there are strategies for avoiding this kind of thing. For instance, you could put a lot of evolutionary energy into becoming very toxic in some way, or having a nasty sting, tasting terrible or some other unpleasant consequence of capture. But that's not the only way — you could also start resembling a toxic, stinging or foul tasting thing, one generation at a time over millenia.
This kind of resemblance between two different species — a model and a mimic — is called mimicry, and it evolves because copycats often gain a survival advantage over species that don't mimic at all. Over time, mimic species start to look more and more like their models. When the mimic is pretty harmless and the model is dangerous or harmful in some way, this is called Batesian mimicry, and it works out pretty well for the mimic, considering how many different organisms do it.
"Batesian mimics are undefended mimics that resemble a defended model, but they are able to receive protection by looking like the defended model," says Susan Finkbeiner, an entomologist and ecologist in the Department of Biological Sciences at California State University, Long Beach. "I've always been fascinated by the many insects that mimic, or resemble, wasps and bees. There are moths and flies that look like bees. There are harmless grasshoppers and beetles that look like wasps. And their resemblance to the wasps and bees is impeccable down to some of the smallest details!"
Batesian mimicry was originally defined in non-predatory animals — it is common in frogs, snakes and butterflies, to name a few. But plants and fungi also try to pass as inedible or toxic stuff: Some plants look like or resemble rocks in order to be less noticed by herbivores. Some fungi that grow on flowers mimic the pollinator-attracting parts of the flower, which results in pollinators spreading the fungal spores in addition to pollen grains when they travel from flower to flower.
According to Finkbeiner, Batesian mimicry only works under the right circumstances. For starters, looking tough, poisonous or disgusting is only effective if a predator actually learns to avoid you because of it. Otherwise your outfit is useless. Secondly, the species the mimic is modeling itself after has to occur in the same geographic area as the mimic — if not, the predators in their area might not even know to avoid them because they hadn't learned to avoid the model species to begin with. And finally, the frequency or number of the model species present in the landscape has to be higher than the number of mimics present – otherwise predators might start to learn that some of the mimics go down pretty smooth.
And while Batesian mimics often stop at looking like the model species, some mimics take Batesian mimicry to the extreme by mimicking even the behaviors of the models: mimicking sounds, flight patterns and antennal movements.
Other Types of Mimicry
Some organisms mimic something completely different from them, like katydids and moths mimicking leaves, or caterpillars and stick insects mimicking twigs.
"Rather than calling this Batesian mimicry, this mechanism is considered 'masquerade' where the organism is masquerading as something that it is not," says Finkbeiner. "Masquerade combined with Batesian mimicry is considered 'protective deceptive mimicry.'"
In another form of mimicry, called Müllerian mimicry, two unrelated dangerous species resemble each other in order to reinforce the "NO TOUCHING" vibe attendant with both, thereby letting potential predators know, this is what danger looks like.